There has been increasing emphasis on the application of robotics technology to various industrial uses. The Robot Institute of America defines a robot as a "reprogrammable, multifunctional manipulator designed to move materials, parts, tools or specialized devices through various programmed motions for the performance of a variety of tasks". The field of robotics is a rapidly developing technological area.
Robots with serial and parallelgram-type direct drive arms have been available before. However, while direct drive arms have certain advantages, they also have some disadvantages. In direct drive arms, the shaft of the motor is connected directly to the component being driven. This eliminates the intermediate transmission or speed reducer and its static load. It also reduces mechanical backlash, cogging, friction and thus wear. Direct drive it also increases structural stiffness of the system. However, elimination of the transmission also means that the motors "see" the full inertial and gravitational forces of the system without any reduction. This, in turn, can cause overheating of the motors, even under only static loading, requiring larger motors and/or amplifiers. Reducing the weight of the mechanical components of the system is of only limited help.
U.S. Pat. No. 4,341,502 to Makino and U.S. Pat. No. 4,552,505 to Gorman show robots with direct motor drives.
The assembly robot of Makino includes an arm comprised of four links, two of which adjacent links are each connected directly to the shaft of separate drive motors.
Various counterbalance arrangements have been provided heretofore. For example, U.S. Pat. No. 3,721,416 to Goudreau shows a loading balancer including a four bar linkage, guide slots and rollers. U.S. Pat. No. 4,229,136 to Panissidi shows a programmable air pressure counterbalance system. U.S. Pat. No. 4,359,308 to Nakajima shows a counterbalance device for a laser knife wherein the centers of gravity of the manipulator and the counterbalance device are moved in the same vertical plane but in opposite, parallel directions. These approaches, however, tend to be relatively complicated and thus expensive. Moreover, these approaches add static weight to the system requiring larger actuators and causing higher dynamic loads which affect overall response and performance.
A need has thus arisen for a statically-balanced direct-drive robot arm which is designed to eliminate gravity forces on the drive system without the expense, complication and dynamic performance drawbacks of a counterbalance arrangement.